In:
Astronomy & Astrophysics, EDP Sciences, Vol. 678 ( 2023-10), p. A68-
Abstract:
We report the discovery of a remarkable Ly α emitting galaxy at z = 7.2782, JADES-GS+53.16746−27.7720 (shortened to JADES-GS-z7-LA), with rest-frame equivalent width, EW 0 (Ly α ) = 388.0 ± 88.8 Å and UV magnitude −17.0. The spectroscopic redshift is confirmed via rest-frame optical lines [O II ], H β and [O III ] in its JWST/NIRSpec Micro-Shutter Assembly (MSA) spectrum. The Ly α line is detected in both lower resolution ( R ∼ 100) PRISM as well as medium resolution ( R ∼ 1000) G 140 M grating spectra. The line spread function-deconvolved Ly α full width at half maximum in the grating is 383.9 ± 56.2 km s −1 and the Ly α velocity offset compared to the systemic redshift is 113.3 ± 80.0 km s −1 , indicative of very little neutral gas or dust within the galaxy. We estimate the Ly α escape fraction to be 〉 70%. JADES-GS-z7-LA has a [O III ]/[O II ] ratio (O32) of 11.1 ± 2.2 and a ([O III ] + [O II ])/H β ratio (R23) of 11.2 ± 2.6, consistent with low metallicity and high ionization parameters. Deep NIRCam imaging also revealed a close companion source (separated by 0.23″), which exhibits similar photometry to that of JADES-GS-z7-LA, with a photometric excess in the F 410 M NIRCam image consistent with [O III ] + H β emission at the same redshift. The spectral energy distribution of JADES-GS-z7-LA indicates a “bursty” star formation history, with a low stellar mass of ≈10 7 M ⊙ . Assuming that the Ly α transmission through the intergalactic medium is the same as its measured escape fraction, an ionized region of size 〉 1.5 pMpc is needed to explain the high Ly α EW and low velocity offset compared to systemic seen in JADES-GS-z7-LA. Owing to its UV-faintness, we show that it is incapable of single-handedly ionizing a region large enough to explain its Ly α emission. Therefore, we suggest that JADES-GS-z7-LA (and possibly the companion source) may be a part of a larger overdensity, presenting direct evidence of overlapping ionized bubbles at z 〉 7.
Type of Medium:
Online Resource
ISSN:
0004-6361
,
1432-0746
DOI:
10.1051/0004-6361/202346245
Language:
English
Publisher:
EDP Sciences
Publication Date:
2023
detail.hit.zdb_id:
1458466-9
SSG:
16,12
